The invention relates to improvements in a pressure regulating valve for a fuel injection system for an explosion, external auto-ignition, internal combustion engine having a suction duct in which there is arranged an air-flow sensor member which is displaced by the amount of air flowing through it against the restoring force produced by the pressure fluid. The arrangement is such that the pressure fluid being continuously conveyed in the control pressure conduit under constant pressure which is changeable at will by means of the pressure regulating valve with the movable valve component of the pressure regulating valve at one side thereof being under the action of the pressure fluid and with that at the other side under the action of the pressure spring so that the force of the pressure spring can be decreased by a temperature-responsive element. Further a pressure regulating valve for a fuel injection system is also known in which the temperature-responsive element is heated up immediately after start by an electrical heating coil, however, this results in a too fast reduction in the fuel enrichment during the heating-up phase.